PP-11681 Replace ‘base-client’ with ‘axios-base-client’

- Change  ‘adminusers.client’ methods to use ‘axios-base-client’.
- Refactor call parameters initialisation.
- Use ‘async/await’ syntax.
- Extend ‘instanceof RESTClientError’ test in registration controller to include a test for constructor name.
  This is order to identify an error thrown by the new 'axios-base-client'. Possibly needs refactoring.

app/controllers/registration/registration.controller.js

@@ -53,7 +53,7 @@ async function submitEmailPage (req, res, next) {
 
     res.redirect(paths.register.checkEmail)
   } catch (err) {
-    if (err instanceof RESTClientError) {
+    if (err instanceof RESTClientError | err.constructor.name === 'RESTClientError') {
       if (err.errorCode === 403) {
         errors[EMAIL_INPUT_FIELD_NAME] = validationErrors.notPublicSectorEmail
         return res.render('registration/email', { errors, email })